A semiconductor memory device, for example, a dynamic random access memory (DRAM) device generally includes: a memory cell array region, a core region, and a peripheral circuit region. The core region includes: a sub-word line driver, a sense amplifier, and a YI transistor. The YI transistor connects a bit line with a segment input/output (I/O) line. Generally, the YI transistor has a wave pattern instead of a straight pattern in order to reduce the size of the core region while ensuring the proper width thereof.
FIG. 1 illustrates a conventional YI transistor.
Referring to FIG. 1, the YI transistor 110 is disposed to cross an active region 105 of a semiconductor substrate 100. In order to ensure an effective channel length while preventing an increase of a chip size, the YI transistor 110 on the active region 105 has a wave pattern that increases the width W1 of the YI transistor 110. As a result, an area occupied by the YI transistor 110 decreases, thereby reducing the size of the core region.
However, when a YI transistor is formed in the wave pattern, there is a difference between the target wave pattern and the final resulting wave pattern in terms of the length of the YI transistor. The length difference may be more than 30 nanometers (nm).
Such the large length difference may affect the characteristics of a semiconductor memory device. More particularly, the large length difference degrades critical dimension uniformity of the wave pattern. In addition, an optical proximity correction (OPC) process is not useful for correcting pattern distortion because of the length difference.